This invention relates to apparatus for energizing a selected one or more of a plurality of actuation devices in order to cause a printing element associated with each selected actuation device to strike an adjacent recording medium.
Matrix printing techniques have been known for many years with the most contemporary methods utilizing a matrix print head having a plurality of printing wires arranged in a linear array at a printing end adjacent a recording medium. A character is printed in a dot matrix, wherein the dots of each of a plurality of columns of dots are formed by impacting selected ones of the wires against the adjacent recording medium. An electromagnetic actuating assembly, usually including an armature, at least one pole piece and a coil disposed about the pole piece, is employed to selectively impact each print wire against the recording medium. These types of print heads are well-known, as exemplified in U.S Pat. Nos. 3,627,096 and 3,929,214.
As discussed in U.S. Pat. No. 3,627,096, it is possible to print letters in both upper and lower-case font style by using two additional print wires positioned below the standard seven at the linearly arranged ends of the wires. The additional wires are necessary since there are some lower-case letters, e.g. "g" and "j," which demand an extension below the normal base line of all upper-case letters and most lower-case letters. Accordingly, and as described in the patent, the first through seventh wires only are used in the formation of all upper-case letters, whereas all nine wires are used to form the lower-case letters.
In view of the above, it is heretofore been found necessary to provide a character memory capable of providing a plurality of bits of data for each dot column to be imprinted, wherein the number of data bits at least equals the number of print wires in the print head. In the print head disclosed in U.S. Pat. No. 3,627,096, which has nine wires, the memory must be capable of supplying nine bits of data for each column of dots to be formed. Although 9-wire memories have been used in the past in connection with hard-wired matrix printer control systems, modern-day microprocessor controllers normally utilize 8-bit memory devices, which may require the need for two such devices (16-bit capacity) in order to provide the requisite 9-bit output. Such use of plural 8-bit memories suffers from the disadvantages of being wasteful, costly and prone to timing errors, since all 9-bits for each dot column must normally be supplied simultaneously, thereby requiring the one bit utilized from the second memory to be synchronized with the eight bits supplied from the first memory.
It would be desirable, therefore, to be able to use a single memory device of a predetermined bit-capacity for controlling the actuation of a plurality of print wires, such as those in a matrix print head, in order to print both upper and lower-case letters, wherein the total number of wires may be more than the bit-capacity of the memory.